Research priorities for the adaptation of agricultural policies and practices to climate change

Pete Smith, School of Biological Sciences, University of Aberdeen

SUMMARY: The steps necessary to reduce greenhouse gas emissions from agriculture are well known, but will not occur unless suitable policies and incentives are put in place to encourage their use by land managers.

Agriculture is a significant source of the three main biogenic greenhouse gases (GHGs), carbon dioxide, nitrous oxide and methane. Within the EU-15, croplands are a significant source of both carbon dioxide (78 Mt C y-1) and nitrous oxide (~60 Mt C-equivalents y-1). Since agricultural management is responsible for much of this flux, there is potential within the EU-15 to reduce this flux or to sequester soil carbon. Many factors drive GHG emissions from agriculture, a significant number of which are socio-political.

Meta-analyses of data in Europe could help to provide better emission factors than current defaults for use in Europe. In the future, dynamic emission factors (that respond to, for example, climate, soils, crop, fertiliser etc.) might replace the static default emission factors currently used. Well-evaluated process-based models, linked to a series of benchmark sites, may play a role in GHG accounting in the future. Verification of GHG emission estimates will be difficult.

Greenhouse gas emissions in 1990 and 2000 for EU-15 are estimated to be as follows: nitrous oxide-1990: 60 Mt C-equivalents y-1, nitrous oxide-2000: 57 Mt C-equivalents y-1, methane-1990: 54 Mt C-equivalents y-1, methane-2000: 50 Mt C-equivalents y-1, carbon dioxide-1990s: 78 Mt C y-1.

A recent study for four country level case studies and the EU as a whole shows that because cropland area is decreasing, and there are no current incentives in place to encourage soil carbon sequestration, carbon sequestration has been small or negative in the EU-15 and all case study countries (with a small level of sequestration in Belgium). The only trend in agriculture that may be enhancing carbon stocks on croplands at present is organic farming, and that is highly uncertain. Previous studies had focused on the potential for carbon sequestration and showed quite significant potential when examining the sequestration likely to occur by 2010, but the recent study suggests that this potential will not be realised. Without incentives for carbon sequestration in the future, cropland carbon sequestration under Article 3.4 of the Kyoto Protocol will not be an option in EU-15.

For reducing emissions of nitrous oxide (and methane) there are a number of options that offer significant GHG mitigation, most of which rely upon better fertiliser (mineral and organic) use and water management. The livestock and manure management sectors offer greater mitigation potential for methane. There may be trade-offs between different greenhouse gases, especially between carbon dioxide and nitrous oxide, so it is important to assess potential mitigation options for their impact upon all greenhouse gases.

Future priorities include the need for a better understanding at the process level (especially in cropland soils), data / inventory collation and meta-analysis, further development of future scenarios of agricultural land-use and management, the development of new technologies and methodologies for measuring soil carbon and greenhouse gas emissions simultaneously, process studies (both modelling and experimental) to couple the carbon and nitrogen cycles and a more complete biogeochemical / physical / socio-economic assessment of GHG mitigation options in agriculture.